As UWB communication becomes increasingly desirable for communication between wireless devices due to its low power, speed, and capacity combined with its resilience to interference within high-frequency bands, design of certain modules associated with the initial Radio Frequency (RF) processing, also referred to as the RF “front end”, becomes a great challenge due to the unique characteristics of the UWB signal environment. In particular, the Automatic Gain Control (AGC) circuit is a common and important RF module whose design poses unique challenges in the UWB environment.
It is understood that several challenges exist in successful AGC module design for UWB systems. Since gain adjustment is generally required to set input levels to conversion stages, such as Analog to Digital conversion stages, the speed of AGC circuits is of critical importance. While certain parameters may be relaxed in connection with UWB AGC requirements, such as, for example, linearity, the speed at which gain of an incoming UWB signal can be adjusted is of critical importance due in large measure to the high frequencies associated with UWB transmission and the commensurate speed required for performing signal processing.
In a related processing procedure, the signal acquisition procedure allows the detection of the beginning of a UWB transmission sequence associated, for example, with a frame transmission, and can provide, for example, a UWB receiver sufficient time to make several measurements in order to attempt to find a multipath component with the most desirable, or stronger, signal. In order to detect the beginning of the UWB transmission sequence or frame, it is important that the preamble common to UWB transmissions and specified in UWB standards, such as standards and definitions put forth by the Institute of Electrical and Electronic Engineers (IEEE), 802.15.3(a) working group, is able to be detected.
In addition to facilitating proper synchronization of the UWB receiver with the received signal phase and the like, the preamble further provides the ability for the receiver to achieve fundamental signal acquisition or signal lock whereby the receiver “locks” onto the signal containing the incoming frame. It will be appreciated that a typical preamble includes a known, recognizable, and repeated pattern of bits that a receiver can easily recognize and therefore detect. It will be appreciated that while, as described, a preamble generally contains a known pattern, the actual starting point within the pattern at which the receiver recognizes or detects the preamble will be random or asynchronous with respect to the actual start of the preamble pattern as transmitted. Thus, once the receiver successfully locks or synchronizes with an incoming preamble, there is generally no way to determine with a high degree of confidence when the end of the preamble will be received and thus how much time remains for the receiver to perform additional functions.
In a narrow band system, a receiver can relatively accurately detect a start time at which carrier energy is detected in the RF environment, allowing a narrowband receiver to determine a preamble start time with a high degree of precision, and the receiver is capable of knowing how much time remains before the end of the preamble is received and more significant information must be received and processed. In a UWB system, however, because the signals have an extremely low signal-to-noise (SNR) ratio, energy detection is difficult and generally undesirable as a solution to accurately detecting the beginning of the preamble.
In UWB receivers requiring additional signal processing or other preparation before receiving information from a frame, problems may arise due to limited detection ability. For example, some operations may be performed to improve signal quality which may require additional training time to operate. As noted, since the UWB receiver does not know how much time remains in the preamble after signal lock, it cannot determine whether there is sufficient time remaining for additional operations.
Accordingly, it would be desirable in the art for a solution to the problems associated with unknown relative signal lock timing, and further to the problems associated with trying to allow adequate time for receiver training when a receiving device has no way of knowing the remaining time in a preamble once signal lock is completed.